How do I create a copy of an object in PHP?

In PHP 5+ objects are passed by reference. In PHP 4 they are passed by value (that's why it had runtime pass by reference, which became deprecated).

You can use the 'clone' operator in PHP5 to copy objects:

$objectB = clone $objectA;

Also, it's just objects that are passed by reference, not everything as you've said in your question...

The answers are commonly found in Java books.

cloning: If you don't override clone method, the default behavior is shallow copy. If your objects have only primitive member variables, it's totally ok. But in a typeless language with another object as member variables, it's a headache.
serialization/deserialization

$new_object = unserialize(serialize($your_object))

This achieves deep copy with a heavy cost depending on the complexity of the object.

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